[13.08] New Observations of the Near Contact Binary XZ Canis Minoris

We present new observations of XZ CMi taken at the National
Undergraduate Research Observatory (NURO). Our CCD
observations were taken 08-12 March 2005 by DRF and NCH with
the Lowell Observatory 31-inch reflector and a LN cooled CCD
camera with a metachrome coated TEK 512 X 512 chip. Standard
UBVRI filters were used. A preliminary light curve analysis
and an updated periodicity study is presented.

XZ CMi [\alpha(2000)=07h 54m 07.056s,\delta(2000)=+03 39
20.32] is a near-contact binary discovered by C.
Hoffmeister (AN 253, 1934). Our light curves show eclipse
amplitudes of magnitudes 0.722 and 0.104 in B and 0.651 and
0.18 in V, for the primary and secondary eclipses,
respectively. The curves are fairly symmetrical, but show
some irregularities, possibly due to solar-type activity. We
took 87 images in B, 78 images in each of VRI, and 27 in U
and determined three eclipse timings. They are HJD Min
I=2453440.6116 ± 0.0003, 2453441.7676 ± 0.0001 and
HJD Min II=2453442.6428 ± 0.0019.

Our periodicity study of the last 25,000 orbital cycles
reveals a rather noisy (R = 0.7) sinusoidal ephemeris: HJD
Hel Min I =2453441.77548±0.0032d +
0.5788087±0.0000002*E + (0.0068±0.0005) Sin[(1.07810
±0.0001)*E+5.8±0.1]. A light time effect indicates
an a(sin i) = 1.17±0.08 AU. Indeed, a third body is seen
in images of XZ CMi in fair to good seeing. On the other
hand, this effect may be due to the solar cycle of XZ CMi or
possibly the period of nodal regression of the orbit. The
period of the oscillation is 25.7 ±0.7 years.

We wish to thank the NURO for their allocation of observing
time, as well as NASA and the American Astronomical Society
for their support in paying for travel and publication
expenses.